DN06002/D Design Note – DN06002/D 1 W, Dual Output, Off-line Converter Device Application Input Voltage Output Power Topology I/O Isolation NCP1012 Auxiliary off-line power supply for appliances 85 to 270 Vac 1W Buck/Flyback None Other Specifications Output Voltage Ripple Nominal Current Max Current Min Current Output 1 Output 2 Output 3 -5V 100 mV 100 mA 100 mA 10 mA - 12 V 200 mV 50 mA 50 mA 0 mA N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A PFC (Yes/No) Passive due to low input C Minimum Efficiency 70% Operating Temp Range Cooling Method/Supply Orientation 0 to +55 °C Convection Circuit Description Key Features This design is intended for low power applications where 5 V and/or 12 V may be necessary for control circuits in appliances or similar devices in which mains isolation is not required and low cost and simplicity are mandatory. The topology is an off-line buck converter configured for a 5 volt negative output with an additional negative 12 volt output derived from a secondary flyback winding on the buck choke. The schematic notes detail how this circuit can be converted for positive outputs if desired. The input section uses half-wave rectification for simplicity and allows the output common to be referenced to the mains neutral line. An input EMI filter is provided for conducted emissions compliance. Good output cross regulation is achieved on the 12 V output with the use of stacked windings in the buck choke. Regulation feedback is achieved with a simple zener diode and optocoupler circuit that also provides the required offset floating for the NCP1012 controller. September 2006, Rev. 1 Output 4 • Extremely simple and cost effective low power supply to provide non-isolated, low voltage outputs. • Good cross regulation due to stacked windings in the buck choke. • Low cost monolithic NCP1012 integrated controller with self-biased Vcc used for buck converter. • EMI filter on AC input for agency compliance. • Output polarities easily reversible without component changes. • Over current protection. • 2 watt capability if NCP1014 is used for U1. www.onsemi.com 1 DN06002/D Schematic 1 D2 L2 L1 R1 15 2W AC input 90 - 285Vac 1 mH C1 100nf "X" 1 D1 MRA4007T3 MURS160T3 R4 1K W2 4 6 C7 330uF 16V - 12 Vdc @ 50 mA C8 0.1uf 50V 3 W1 3.5 mH - 5 Vdc @ 100 mA C6 C2 D3 MURS160T3 10 uF 400V C5 NCP1012 (SOT-223) 3 MMSZ5229B 2 4 1 U2 1 C4 C3 47uF+ 16V NOTES: Com R5 (Vtrim) 0 ohm U1 4 0.1uf 50V 470 uF 6.3 Vdc 470pF 3 opto R2 47 Z1 4.3V R3 220 2 1. Crossed lines on schematic are not connected. 2. U1 should have ground tab (pin 4) soldered to expanded ground plane area for good heatsinking (SOT-223 recommended package). 3. U2 is Vishay H11A817A optocoupler or equivalent 4. R1 provides inrush limiting at turn-on (optional). 5. C5 capacitance value dependent on max Vout ripple; 470 uF min recommended. 6. L1 is Cooper/Bussmann UP2B-102R inductor (Uni-Pac series - 1 mH, 0.3 A) or similar. 7. L2 is P18/11/I ferrite core (1811 pot core without hole) on 6 pin pc mount bobbin; W1 is 92 turns of #32HN (0.25 mm dia) magnet wire wound over 4 layers (23 turns per layer). W2 is 115 turns of #32 HN magnet wire woundover 5 layers (23 turns per layer). Core should be gapped to give an inductance of 3.4 to 3.6 mH across W1. 8. R5 is option voltage trim resistor - increasing resistance increases Vout. 9. For positive outputs: reverse diodes D1, D2, and D3; apply dc input to pin 3 of U1 and output will be on pin 4; reverse voltage sensing so cathode of zener goes to 5V output and pin 2 of U2 (opto) goes to output common; reverse polarity of input and output caps C2, C5 and C7. NCP1012 1 Watt, Dual Output Converter ON Semiconductor Applications Group 1 © 2006 ON Semiconductor. Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its products at any time, without notice. Design note created by Frank Cathell, e-mail: [email protected] September 2006, Rev. 1 www.onsemi.com 2